Method of making an ion reflectron comprising a flexible circuit board

ABSTRACT

A novel technique utilizing the precision of printed circuit board design and the physical versatility of thin, flexible substrates is disclosed to produce a new type of ion reflector. A precisely defined series of thin conductive strips (traces) are etched onto a flat, flexible circuit board substrate. Preferably, the thin conductive strips are further apart at one end of the substrate and get increasingly closer towards the other end of the substrate. The flexible substrate is then rolled into a tube to form the reflector body, with the conductive strips forming the rings of the ion reflector. The spacing between the traces, and hence the ring spacing, can be readily varied by adjusting the conductor pattern on the substrate sheet during the etching process. By adjusting the spacing between the rings, the characteristics of the field created by the reflectron can be easily customized to the needs of the user.

This application is a divisional of application Ser. No. 09/639,145,filed on Aug. 16, 2000, now U.S. Pat. No. 6,369,383, benefit ofprovisional application No. 60/149,103 filed Aug. 16, 1999 the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Time-of-Flight (TOF) massspectrometer and, more particularly, to a novel ion reflectron useablein, for example, a TOF mass spectrometer and a method of manufacturingsame.

2. Description of the Related Art

A spectrometer is an analytical instrument in which an emission (e.g.,particles or radiation) is dispersed according to some property (e.g.,mass or energy) of the emission and the amount of dispersion ismeasured. Analysis of the dispersion measurement can reveal informationregarding the emission, such as the identity of the individual particlesof the emission.

It is well known that energy applied to ionized particles (ions) via anelectric field will cause the ions to move. This principle is used indifferent kinds of spectrometers to accomplish different goals. Forexample, an ion mobility spectrometer (IMS) is used to detect andanalyze organic vapors or contaminants in the atmosphere. As describedand shown in U.S. Pat. No. 5,834,771 to Yoon et al, a typical IMSdetector cell (also called an ion drift tube) comprises a reactionregion for generating ions, a drift region or drift tube for separatingions, and a collector.

A carrier or drift gas along with a sample gas introduced into the IMSare ionized and then the sample is moved through the drift tube by anelectric field applied along the drift tube. Different ions in thesample are separated based on their behavior in the drift tube as theycollide with the drift gas. Each type of ion exhibits its ownidentifiable behavior pattern based on its particular structure, e.g.,each ion shows unique velocity due to its mass, size, and charge. Theseparated ions proceed further down the drift tube and collide with thecollector, producing a measurable current. The drift velocities and thepeak currents of the ions arriving at the collector provide a basis forapproximating the identity of the samples introduced into the reactionregion; however, it is not an exacting technique, since two differention types having similar masses and similar interaction with the driftgas will be difficult, if not impossible, to distinguish from eachother.

A variety of methods of generating the electrical field used in thereaction region and the drift tube are available, as described in thepreviously-mentioned '771 patent. The subject matter of the '771 patentis directed to one such method involving the fixation of a flexibleprinted circuit board onto the surface of the drift tube. Evenly-spacedparallel conductive bands are patterned on the flexible circuit boardand the electrically conductive bands are connected to adjacent bandsvia resistances. Through proper biasing of the resistors, the conductivebands are placed at potentials relative to their positions along thetube, so that a uniform electric field is developed along the axis ofthe tube.

Mass spectrometry is another well-known spectrometry method. Massspectrometers are used to determine, with precision, the chemicalcomposition of substances and the structures of molecules. One type ofmass spectrometer, a time-of-flight (TOF) mass spectrometer, is aninstrument that records the mass spectra of compounds or mixtures ofcompounds by measuring the times (usually of the order of tens tohundreds of microseconds) for molecular and/or fragment ions of thosecompounds to traverse a (generally) field-free drift region within ahigh vacuum environment. TOF mass spectrometers operate based on theprinciple that, when ions are accelerated with a fixed energy, thevelocity of the ions differ dependant exclusively on mass and charge.Thus, the time-of-flight from point A to point B will likewise differdependant on the mass of the ion. Using a TOF mass spectrometer, themass of an ion can be calculated based upon its time of flight. Thereare no collisions with a carrier gas as occurs in an IMS—only thevelocity, and therefore the mass and charge (usually +1), is utilizedfor the calculation. This allows the molecule to be identified withprecision.

TOF mass spectrometers are comprised of a source region, where neutralmolecules are ionized, a drift region, followed by an ion reflector(also known as a reflectron) and a detector. In the ion source, ions areformed in a high vacuum environment followed by acceleration down afield free drift region. The ions separate in time dependent only ontheir mass/charge ratio (normally the charge is +1). Upon entering theopposing field created by the ion reflector, ions gradually slow down,stop, and reverse direction. The detection occurs after the ions arere-accelerated out of the ion reflector. In addition to enabling thecalculation of the mass of the ions, ion packet peak widths aresharpened by their passage through the ion reflector, resulting in anenhancement of the instrument's resolving power.

Reflectrons have been in use since the late 1960's and are typicallyconstructed by configuring plural individually manufactured metallicrings along ceramic rods using insulating spacers to separate each ringfrom the next. This technique is labor intensive, costly, and limits theflexibility of design due to the manufacture and handling of extremelythin rings (a few mils in thickness) of relatively large diameter (1″ orgreater). An example of such a configuration is shown in U.S. Pat. No.4,625,112 to Yoshida,. While many permutations of this device exist, themethod of construction has been limited to the ring method describedabove.

Similar to the parallel conductive traces of the '771 patent, the ringsare placed at potentials that develop electric fields along the axis ofthe cylinder. However, in contrast to the IMS method, which develops auniform electric field along the drift tube and which can onlyapproximate the identity of molecules in a sample, a TOF massspectrometer is capable of measuring atomic and molcular weights withhigh precision. Furthermore, to improve performance in a TOF massspectrometer, reflectrons have been constructed which developnon-uniform fields along the reflectron tube. The non-uniform fields aregenerated by utilizing a voltage divider network which varies thepotential applied to each of the evenly-spaced rings. A detailedexplanation of non-linear reflectron theory can be found in U.S. Pat.No. 5,464,985 to Cornish et al., incorporated fully herein by reference.

While the above-described TOF mass spectrometer design has proved quitesatisfactory for large reflectors in which the rings are relativelylarge in diameter and equally spaced, new applications utilizing remoteTOF mass spectrometers may require miniaturized components, ruggedconstruction, and/or the use of lightweight materials. Smaller TOF massspectrometers have reduced drift length, necessitating the use of idealenergy focusing devices (reflectrons) to maximize resolution.

Therefore, it would be desirable to develop new methods of constructionto fabricate miniature ion reflectors for TOF's which are smaller,rugged, and lightweight and which provide maximum resolution.

SUMMARY OF THE INVENTION

To this end, a novel technique utilizing the precision of printedcircuit board design and the physical versatility of thin, flexiblesubstrates has been devised to produce a new type of ion reflector. Inthis method, a precisely defined series of thin conductive strips(traces) are etched onto a flat, flexible circuit board substrate. Theflexible substrate is then rolled into a tube to form the reflectorbody, with the conductive strips forming the rings of the ion reflector.The spacing between the traces, and hence the ring spacing, can bereadily varied by adjusting the conductor pattern on the substrate sheetduring the etching process.

The present invention is a multi-layered reflectron for a time-of-flight(TOF) mass spectrometer, comprising: plural structural layers; and atleast one flexible electrode layer, the flexible electrode layercreating an electric field in the reflectron when a voltage is appliedthereto to slow down, stop, and reverse the direction of travel of ionstraveling through said reflectron. The flexible electrode layercomprises a flexible substrate having a plurality of conducting tracesformed thereon, the flexible substrate being rolled into a tubular shapeso that said conducting traces form rings surrounding a central axisthrough the length of the reflectron. The distance between theconducting traces, and therefore the rings, can, if desired, graduallydecrease from one end of the reflectron to the other. The distancebetween the conducting traces can also be equally spaced, or userdefined (any spacing desired).

The method of manufacturing a reflectron according to one representationof the present invention can comprise the steps of: photo-etching aplurality of conducting traces onto a flexible substrate sheet; wrappingthe photo-etched substrate sheet around a mandrel so that the pluralconducting traces coincide to form a plurality of rings surrounding themandrel, leaving a connector end of the flexible substrate sheetunwrapped; wrapping one or more plies or layers of uncured,pre-impregnated composite material around the substrate, so that all ofthe exposed portion of the substrate, except for the unwrapped connectorend, is covered by the composite material ply(s); curing thephoto-etched substrate and composite material on the mandrel; andremoving the cured photo-etched substrate and composite material fromthe mandrel to form a rigid tubular reflectron.

These objects, together with other objects and advantages which will besubsequently apparent, reside in the details of construction andoperation as more fully described and claimed hereinafter, referencebeing had to the accompanying drawings forming a part hereof, whereinlike reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flexible circuit board substrate prepared accordingto a first fabrication step of the present invention;

FIG. 2 illustrates a second fabrication step in accordance with thepresent invention

FIG. 3 illustrates a third fabrication step in accordance with thepresent invention;

FIG. 4 illustrates a reflector assembly fabricated in accordance withthe steps illustrated in FIGS. 1-3;

FIG. 5 illustrates that a connector end of the flexible circuit board ofthe present invention can be terminated at a rigid circuit portion; and

FIG. 6 illustrates that the flexible circuit board of the presentinvention can be split into multiple segments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a circuit board substrate 100 prepared according to afirst step of the present invention. In accordance with the presentinvention, parallel conductive traces 102 (50 traces are illustrated inFIG. 1 for purpose of example) are etched into the flexible circuitboard substrate material using conventional etching methods. In theexample shown in FIG. 1, a connector end 104 of the conducting traces102 is etched such that the conducting traces 102 are angled at atapered section 106. This allows the conducting traces 102 to convergeat connector end 104 so that at a connector section 108, they are closertogether and properly aligned, thereby allowing for easy attachment of aconnector (not shown).

In one representation of the present invention, the circuit boardsubstrate 100 comprises copper clad Kapton (manufactured by Dupont)polyimide film approximately 0.002″ thick, and the conductive traces 102etched onto the circuit board substrate 102 are approximately 0.008″wide by 0.001″ thick. The distance between each conductive trace can beuniform or, as shown in FIG. 1, can be narrower between some traces andwider between others. The distance between the rings in a reflectrontube affects the field generated by the tube, and thus the distancebetween the traces or the width of the traces can be adjusted accordingto the needs of the end-user. Further, as discussed in more detailbelow, traces A and B on either end (see FIG. 1) may be wider than theother traces to facilitate electrical connections to the outermost ringswhen fabrication of the reflectron is completed.

Once the flexible circuit board substrate 100 has been etched asdescribed above it is rolled into the shape of a tube and supported inthis tubular shape in a rigid fashion. While supporting the tube in arigid fashion is not required, doing so will assure symmetry of therings formed by the rolling of the flexible circuit board substrate 100,which results in precision with respect to the field generated by therings.

Referring now to FIGS. 2 and 3, given as examples. In FIG. 2, theflexible circuit board substrate 100 is rolled around a mandrel 210 toform the tubular shape. When the flexible circuit board substrate 100 isrolled around mandrel 210, each trace aligns with itself to form therings required to create the fields. Due to the thinness of the flexiblecircuit board 100, there is no need to electrically connect the ends ofeach trace; they are at the same potential assuring a continuous fieldinside the tube.

Next, layers of uncured, pre-impregnated fiberglass are wrapped aroundthe flexible circuit board substrate 100 which is wrapped around themandrel 210 (FIG. 3). In FIG. 3, five fiberglass plies 312, 314, 316,318, and 320, each approximately 0.010″ thick, are used. The dimensionsof the fiberglass plies should be such that their width equals orexceeds the distance “W” of FIG. 1, and their length is approximatelyequal to the circumference of the mandrel 210.

By using fiberglass plies having this length, when the plies are wrappedaround the rolled flexible circuit board substrate 100, a slight opening324 exists through which the connector end 104 of the flexible circuitboard substrate 100 can extend. To allow the flexible circuit boardsubstrate 100 to follow its natural shape and thus minimize creasing, inthe second embodiment the starting position of each successivefiberglass ply is moved slightly with respect to the previous ply sothat a gradual “ramp” 326 is formed, thereby creating a gradual anglingof the flexible substrate 100 away from the mandrel 210 as shown.

Once the reflector assembly is formed as described above, the assemblyis cured under heat and pressure in a known manner for approximately twohours. Then the assembly is allowed to cool and the mandrel 210 isremoved. It should be noted that other materials can be used that do notrequire curing with heat and pressure. Therefore, the type of materialused in the assembly dictates the type of curing. The final wallthickness of the rolled reflector assembly constructed in this manner isapproximately 0.060″. A reflector assembly fabricated according to thepreviously described steps is shown in FIG. 4. A standard connector 430,such as a standard 50 pin ribbon connector may be coupled to theconnector end 104 so that the reflectron can be easily incorporated intoa mass spectrometer or any other device requiring a reflectron. Ifdesired, end caps, (e.g., polycarbonate plugs, not shown, or othersuitable material) can be installed on either end of the reflectron toboth support the reflectron in the vacuum chamber of the massspectrometer and to provide a surface on which to affix grids. As iswell known, the grids define and shape the field of the massspectrometer and are usually made of stainless or nickel and/or etchedwire electrically connected to traces A and B. The larger width oftraces A and B maximizes the integrity of the electrical connectionbetween the grid/caps and the traces. The cylindrical shape of thesupport tube and integral ring structure allows the grid/caps to befabricated in many different configurations, e.g., as disk inserts oroverlapping caps. If desired, relief grooves can be machined in thecylinder to ensure appropriate positioning of such a cap or grid.

Reflectors produced according to the present invention are verylightweight, extremely rugged, and inexpensively and easily massproduced. Additional advantages over the prior art include: greaterdesign flexibility in selecting ring width and spaces; no need tohand-assemble the rings as is required by the prior art; the spacing andwidth of and distance between the rings can be easily controlled byreproducible photo lithographic processing or other appropriateprocessing depending on the material used; lithographic patterns orother patterns produced are scalable for various applications usingsimple computer-aided design techniques; reflectron replacement can beeasily accomplished because of the plug-in nature of the reflectron; anduse of high Tg circuit board material allows operation of the reflectronover wide temperature ranges.

While the present invention is described herein in connection with a TOFmass spectrometer, a reflectron fabricated in accordance with thepresent invention can be used in connection with any device requiringthe creation of electrostatic fields, and particularly in devicesrequiring precision, rugged, lightweight, inexpensive, modular, and/ormass producible construction. Further, while a cylindrical reflectron isdescribed herein and shown in the drawings, with simple modifications tothe circuit mask, other geometrical shapes, such as conical reflectors,can also be fabricated with high precision.

While the above-described process uses cured fiberglass layers toprovide the rigid tubular support required for use as an ion reflector,any cured composite material that can be wrapped or rolled around therolled flexible circuit board will suffice. Further, the etched flexiblecircuit board can be formed as a rigid tube using any method whichresults in a rigid tube having the rings formed along the interior ofthe tube. For example, instead of using the fiberglass layers asdescribed above, the etched flexible circuit board could be glued(laminated) to the inside of an appropriate diameter support tube. Thesupport tube could be made of metal or composite materials, dependingupon the required operating conditions. To enable the connector end ofthe flexible circuit board to extend outside of the tube, the tube couldbe provided with a slot that runs almost the entire length of the tube.This slot serves the same purpose as the opening 324 of FIG. 3, i.e., itallows one end of the flexible circuit board to extend through the tubeto permit easy wire attachment or connector attachment to the individualrings formed on the inside of the tube.

FIG. 5 shows that, if desired, the connector end 104 of flexible circuitboard 100 can be terminated at a rigid circuit board portion 530 asshown. Rigid circuit board portion 530 can accommodate, for example, avoltage divider network 532 (i.e., the precision resistors and theinterconnection pattern necessary to apply a specified voltage to eachof the rings). The incorporation of the voltage divider network 532 ontothe same structure as the ring assembly allows the entire reflectron tobe easily replaced by simply disconnecting the assembly from the twoleads 534 and 536 connecting the voltage divider network to the highvoltage power supply. Configured in this manner, a simple two-pinconnector is all that is required (to make the high voltage power supplyconnection).

If it is necessary to reduce the weight of the reflectron tube evenfurther, as illustrated in FIG. 6, the circuit board 100 may be splitinto multiple segments as it exits the reflectron tube and is passedthrough multiple slots 640; the multiple slots 640 create interveningslot supports 642, which provide additional rigidity to the structurewhile still allowing access to make electrical connections to theconductive traces 102.

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and applications shown anddescribed. Accordingly, all suitable modifications and equivalents maybe resorted to, falling within the scope of the invention and theappended claims and their equivalents.

What is claimed is:
 1. A method of manufacturing a reflectron,comprising the steps of: wrapping a flexible circuit board around amandrel, leaving a connector end of said flexible circuit boardunwrapped; wrapping one or more plies of uncured composite materialaround said circuit board, so that all of the exposed portion of saidcircuit board, except for said unwrapped connector end, is covered bysaid composite material ply(s); curing said composite material on saidmandrel; and removing said flexible circuit board and composite materialfrom said mandrel.
 2. A method of manufacturing a reflectron as setforth in claim 1, wherein said composite material comprises fiberglass.3. A method of manufacturing a reflectron as set forth in claim 1,wherein said reflectron forms a circular cylinder.
 4. A method ofmanufacturing a reflectron as set forth in claim 1, wherein saidreflectron forms a rectangular cylinder.
 5. A method of manufacturing areflectron, comprising the steps of: photo-etching a plurality ofconducting traces onto a flexible substrate sheet; wrapping saidphoto-etched substrate sheet around a mandrel so that said pluralconducting traces coincide to form a plurality of rings surrounding saidmandrel, leaving a connector end of said flexible substrate sheetunwrapped; wrapping one or more plies of uncured, pre-impregnatedcomposite material around said substrate, so that all of the exposedportion of said substrate, except for said unwrapped connector end, iscovered by said composite material ply(s); curing said photo-etchedsubstrate and composite material on said mandrel; and removing saidcured photo-etched substrate and composite material from said mandrel toform a rigid tubular reflectron.
 6. A method of manufacturing areflectron as set forth in claim 5, wherein said pre-impregnatedcomposite material comprises fiberglass.
 7. A method of manufacturing areflectron as set forth in claim 5, wherein said rigid tubularreflectron forms a circular cylinder.
 8. A method of manufacturing areflectron as set forth in claim 5, wherein said rigid tubularreflectron forms a rectangular cylinder.